Hi There,

As I understand this so far my Rx gives a PWM signal thats 2.90V peak and varies it in width from 1.0 to 1.8 mS (without trims etc) and my APM2 does about the same at 5.23Volts.

None of my servos respond to this signal.


             Min              Neutral             Max                Peak V

APM      1.2ms             1.8ms            2.0ms               5.23

   RX      1.0ms             1.4ms            1.8ms               2.90

All the first 4 outputs vary in width properly but they are the wrong peak voltage!

Any ideas anybody?

Thanks John Fletcher

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John, Did you ever find an answer? I have a similar question.


Hi Todd,

No, I don't understand why explaining this was so hard or what harm could have been done it's a simple question.

Regards John


I think that you have not had a reply because, apparently, few people understand the details of the signals between receivers and servos. This is, in part, because the manufacturers don't publish these details. It is proprietary. (I.e. they want people to use their servos with their receivers.)

Here is what I have found by looking at the signals with a scope and some reading:

The typical PWM signal from a Rx used to be a nominal 5 Volts. Newer Rx and servo products use a nominal 3.3 V (CMOS level) signal.

I just tested some small Eflite servos and they are able to read both levels. (3 and 5 V)

As far as I can tell, there is no easy way (if any) to tell the APM to drive the output signals at 3.3 V. (Take this with a grain of salt, because I am new to this.)


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